White blood cells are an important part of your body’s immune system. They are vital for protecting you from invading bacteria or parasites. Your body is host to five different kinds of white blood cells, all of which are made in the bone marrow.
Each white blood cell lives for three to four days, then is replaced. How many white blood cells and what type you have in your body can give doctors a better understanding of your health. Elevated levels of white blood cells in your blood are a good indicator that you are suffering from an illness. This is because it means your body is sending more and more white blood cells to fight off infections.
An eosinophil count is a type of blood test that measures the quantity of eosinophils (a type of white blood cell) in your body. An eosinophil count is typically used to confirm a diagnosis rather than make a diagnosis. According to the American Association of Clinical Chemistry, eosinophils are particularly involved in immune responses to infections caused by parasites and allergic reactions (AACC, 2012).
Eosinophils have two distinct functions in your immune system. First, they destroy invading germs like viruses, bacteria, or parasites such as Giardia and pinworm. Eosinophils also create an inflammatory response.
Inflammation is both good and bad. It helps isolate and control the immune response at the site of an infection, but it also damages the tissue around it. Allergies are immune responses that often involve chronic inflammation. Eosinophils play a significant role in the inflammation related to allergies and asthma.
Your doctor may recommend an eosinophil count if you have already had a blood differential and the results were abnormal. A blood differential test determines the percentage of each kind of white blood cell present in your blood. This test will show if you have an abnormally high or low count and if you have abnormal cells that are associated with various diseases.
Your doctor may also order this test to help confirm the diagnosis of certain diseases or conditions, such as:
- an extreme allergic reaction
- the initial stages of Cushing’s disease (a disorder caused by too much of the steroid hormone cortisol)
- a parasitic infection
Your doctor will need to take a sample of blood from your arm. First, the site will be cleaned with a swab of rubbing alcohol. The needle will then be inserted into a vein and a tube will be attached to fill with blood. When enough blood has been drawn, the needle will be removed and the site will be covered with a pad. The blood sample will then be sent to a laboratory for analysis.
A normal blood sample reading will show fewer than 350 eosinophil cells per microliter of blood.
High numbers of eosinophil cells—a disorder known as eosinophilia—can be caused by any of the following:
- an allergic reaction to parasitic worms
- an autoimmune disease
- seasonal allergies
- ulcerative colitis
- scarlet fever
- Crohn’s disease
An abnormally low eosinophil count can be caused by intoxication from alcohol or excessive production of cortisol (a steroid produced naturally in the body).
An eosinophil count is performed using a standard blood draw, which you have likely had many times in your life.
As with any blood test, there are minimal risks of experiencing minor bruising at the needle site. In rare cases, the vein may become swollen after blood is drawn. This condition, known as phlebitis, can be treated with a warm compress several times each day.
There are no special preparations necessary for this test. You should inform your doctor if you are taking any blood-thinning drugs such as warfarin (Coumadin). Your doctor may advise you to stop taking certain medications.
Medications that may cause you to have an increased eosinophil count include:
- appetite suppressants
- interferon (a drug used to help treat infection)
- some antibiotics
- laxatives that contain psyllium
Be sure to mention any current medication with your doctor before the test.
If you are suffering from an allergy or parasitic infection, your doctor will prescribe a short-term treatment to alleviate symptoms and revert your white blood cell count to normal.
If an autoimmune disease is indicated, your doctor may want to conduct more tests to determine which type of diseases you are suffering from. He or she may then prescribe corticosteroids.